THURSDAY, July 17, 2014 (HealthDay News) -- The nation's supply of registered nurses has been growing faster than expected, largely because baby boomers in nursing are working longer than ever before, according to a new study.

Due to both the delayed retirement of experienced nurses and a surge in new nursing graduates, there were almost 3 million nurses in the United States in 2012, about half a million more than estimated a decade ago.

Exactly why baby boomer nurses aren't retiring isn't known. But it could be that they are part of a trend among other Americans, particularly women, said David Auerbach, senior policy researcher at the RAND Corporation in Boston. "They may be staying in the workforce because of their longer life expectancy and the satisfaction they get from being employed."

Auerbach suggested that it's possible that the trend is part of a shift that is bigger than nursing and more about the position of women in the workforce. "They are mirroring the position of men, working longer, especially in challenging economic times," he said.

The trend of registered nurses (RNs) delaying retirement has extended the average nursing career by 2.5 years after age 50, and increased the 2012 workforce by 136,000 registered nurses, according to the research.

The size of the registered nurse workforce is particularly sensitive to changes in retirement age, given the large number of baby boomer nurses now employed. About 74 percent of those nurses who are 62, and 24 percent who are 69 are still working, the researchers noted.

While it may be a positive thing for seasoned nurses to stay in their jobs longer, new graduates are finding it harder to get work, experts said.

A nursing shortage in the late 1990s, coupled with the anticipation of baby boomer nurses retiring in droves, spurred colleges to expand nursing education programs after 2000, said Auerbach. "Between 2002 and 2012 the number of nursing school graduates doubled," he said.

But the Great Recession that began in 2008 may have changed the retirement plans of many nurses, who might have seen their retirement funds plummet, had unemployed or underemployed spouses and, possibly, adult children returning home, said Judee Berg, executive director and president of the California Institute for Nursing and Health Care.

At the same time, the health care system has been retooling in response to implementation of the Affordable Care Act, aiming to reduce the number of days people are hospitalized and putting more emphasis on outpatient and home care, said Berg. That means some new graduates of nursing programs are finding hospital jobs harder to find, she added.

But experts are predicting an emerging new shortage -- a perfect storm -- when the economy improves, boomer nurses finally retire and the entire generation of baby boomers are seniors. Data from the U.S Census Bureau show there are more than 76 million baby boomers in the United States. "There is a real concern that there is a pent-up retirement that is going to happen," Berg said.

Even now, the job shortage for new nurses is not universal. Some regions of the United States -- Texas, Florida and North Dakota -- have many jobs available for new graduates, Berg said.

Information for the study came from the American Community Survey (ACS) and the Current Population Survey (CPS), from 2001 to 2012. The data included all respondents aged 23 to 69 who reported being employed as a registered nurse during the week of the survey.

The CPS surveys more than 100,000 people and is administered by the Census Bureau; it provides data on about 3,000 to 4,000 registered nurses per year. The ACS survey included up to 30,000 registered nurses for the sample period. The data was used to estimate the number of full-time nurses working each year and their ages.

For the time being, the trend means that consumers of health care will likely have more experienced and knowledgeable nurses, both in hospitals and in community and home care settings, said Berg.

"Patients will probably notice just a continued graying of the nurses they see," echoed Auerbach.

The study findings were published online July 16 and in the August print issue of the journal Health Affairs.